The conventionally-known cogeneration apparatus are combined heat and power apparatus which include an engine, power generator and heat exchanger provided within an apparatus casing, and in which exhaust heat of an engine driving the power generator is collected and the collected heat is used for heating the interior of a room and the like. An example of such cogeneration apparatus is disclosed in Japanese Patent Application Laid-Open Publication No. 2007-187027, which, because the engine, power generator and heat exchanger are provided within the apparatus casing, is constructed to ventilate the air within the casing to thereby keep optimal an environment temperature within the casing.
Among other examples of the conventionally-known cogeneration apparatus is one which includes a CO sensor for detecting carbon monoxide (CO) contained in exhaust gas. When exhaust gas has flown out to within the casing, carbon monoxide (CO) contained in the exhaust gas is detected by the CO sensor, so that the engine is deactivated in response to CO detection information output from the CO sensor. However, in order for the CO sensor to detect carbon monoxide (CO) contained in the exhaust gas, it is necessary that a certain amount of exhaust gas be stored within the casing. Therefore, the exhaust gas stored within the casing may flow out of the casing before the CO sensor detects carbon monoxide in the exhaust gas flown out to within the casing. If the cogeneration apparatus is installed indoors, the exhaust gas may undesirably flow out of the casing to an indoor area.